A carbon nano structure designates a nano size material constituted of carbon atoms. Examples of carbon nano structure includes carbon nanotube; carbon nanotube with beads, which is a carbon nanotube in which beads are formed; a brush-shaped carbon nanotube constituted of a forest of carbon nanotubes; carbon nanotwist, which is a twisted carbon nanotube; a coil-shaped carbon nanocoil; and spherical shell fullerene.
Carbon nanocoil was synthesized for the first time in 1994 by way of Chemical Vapor Deposition (hereinafter referred to as a CVD method) by Amelinckx, and some other researchers (Amelinckx, X. B. Zhang, D. Bernaerts, X. F. Zhang, V. Ivanov and J. B. Nagy, SCIENCE, 265 (1994) 635). It was also found that, in contrast to the conventional carbon microcoil of amorphous structure, a carbon nanocoil has a graphite crystal structure.
In the method of Amelinckx and others, a single metal catalyst such as Co, Fe, or Ni was processed into fine powder, and the vicinity of the catalyst was heated to 600 to 700° C., and an organic gas such as acetylene or benzene was put into circulation in it to come in contact with the catalyst, so as to decompose the organic molecules. However, according to this method, the shapes of the resulting carbon nanocoils were uneven, and the yield was low. It was therefore assumed that the production was incidental, that is, it was not reliable as industrial production. Therefore there has been a demand for a more efficient method.
In 1999, Li and some other researchers (W. Li, S. Xie, W. Liu, R. Zhao, Y. Zhang, W. Zhou and G. Wang, J. Material Sci., 34 (1999) 2745) succeeded to produce a new carbon nanocoil. According to their method, a catalyst constituted of a graphite sheet with a periphery coated with iron particles was placed in the center, and the vicinity of the catalyst was heated to 700° C. by a nichrome wire. Then a mixture gas of 10% of acetylene and 90% of nitrogen gas in volume was brought into contact with the catalyst to be reacted with the catalyst. However, this method does not ensure a desirable coil yield, and was not sufficient as industrial production.
The key of increase in yield of carbon nanocoil in a CVD method is development of appropriate catalyst. In this view, a part of the inventors of the present invention developed a Fe—In—Sn type catalysts by which the yield increased to 90% or greater. The method is published in Japanese Laid-Open Patent Publication Tokukai 2001-192204 (Patent Document 1: published on Jul. 17, 2001). The catalyst was constituted of an ITO (Indium-Tin-Oxide) substrate on which a mixture thin film of In oxide and Sn oxide is formed and an iron thin film is formed thereon by vapor deposition.
Further, a part of the inventors of the present invention produces Fe—In—Sn type catalysts by an alternative method and succeeded to invent mass production of carbon nanocoil. The invention is disclosed in Japanese Laid-Open Patent Publication Tokukai 2001-310130 (Patent Document 2: published on Nov. 6, 2001). In this case, to produce the catalyst, In organic compound and a Sn organic compound was mixed with an organic solvent to prepare an organic liquid, and the organic liquid was applied on a substrate to form an organic film. Then the organic film was calcined to form a In/Sn oxide film, and an iron thin film was formed on the In/Sn oxide film. The In/Sn oxide film corresponds to the aforementioned ITO film (mixture thin film).
Meanwhile, a part of the inventors of the present invention published a mass production method of carbon nanocoil by catalyst distribution (Japanese Laid-Open Patent Publication Tokukai 2003-26410 (Patent Document 3: published on Jan. 29, 2003)). In this CVD method using catalyst vapor-phase transfer, a hydrocarbon gas was supplied to a heated reactor made of a vertically-placed quartz tube and put into circulation, and the catalyst particles are dispersed in the gas. Then a carbon nanocoil was grown on the surfaces of catalyst particles while the hydrocarbon is decomposed in the vicinity of the catalyst. This method using the dispersed catalyst allows highly-dense growth of a carbon nanocoil. By repeating growth and collection of carbon nanocoil, sequential production of carbon nanocoil becomes possible. Another CVD method using a vertical reactor tube is disclosed in Tokukai 2003-138432 (Patent Document 4: published on May 14, 2003)) which adopts a force feed manner in supplying a material gas into a reactor. In this method, a material gas is sprayed into a reaction region of the reactor tube via a supply nozzle.
[Patent Document 1] Tokukai 2001-192204
[Patent Document 2] Tokukai 2001-310130
[Patent Document 3] Tokukai 2003-26410
[Patent Document 4] Tokukai 2003-138432